1. Field of the Invention
The present invention generally relates to a method of optical proximity correction (OPC), and more particularly, to a method of OPC which comprises more than one OPC model.
2. Description of the Prior Art
With the trend of miniaturization of the electronic products and peripherals, research about thin structures and high integration of the semiconductor devices have become the essential subjects and developing aspects in the industry, and the lithography technology plays an important role to determine the performances of the semiconductor devices.
In semiconductor manufacturing processes, the integrated circuit layout is first designed and formed as a mask pattern. The mask pattern is then proportionally transferred to a photoresist layer disposed on the semiconductor wafer through an exposure process followed by a development process. Subsequently, a corresponding etching process is performed in order to manufacture the semiconductor devices on the semiconductor wafer. With the demand of increasing integration and the decreasing size of the semiconductor devices, the critical dimension (CD) of each segment fabricated through exposure is limited to the resolution limit of the optical exposure tool used for transferring the mask pattern. The optical proximity effect is a problem that easily arises during the exposures of a mask pattern with high-density arranged segments to form a pattern on a photoresist. Such a resolution loss occurs because of overexposure or underexposure, which brings a deviation of the pattern on the photoresist layer from the original mask pattern. Many methods have been used to avoid the deviation caused by the optical proximity effect in order to improve the quality of the transferred pattern. The most popular method is the optical proximity correction (OPC). And there is a variety of commercial optical proximity correction software that can theoretically correct the mask patterns to be more accurately transferred on a wafer.
Currently, a modeled-based optical proximity correction method, which uses optical proximity correction models to simulate the final mask pattern needed to be transferred to the corresponding photoresist layer, is widely used in processes for manufacturing semiconductor devices. Generally, various optical proximity correction models are provided in order to fulfill the needs of various mask patterns. For example, when an original layout pattern corresponding to a M0 structure of a semiconductor device needs to be formed in a semiconductor device, this pattern must be simulated by an optical proximity correction (OPC) method based on a proper optical proximity correction model in order to output a corrected pattern (i.e. a corrected M0 pattern) into a photomask. However, the OPC method, which is based on only one kind of OPC model, can not fulfill the needs of the M0 pattern including different geometric patterns with various length-to-width ratios. Accordingly, some patterns transferred from the photomask to a photoresist layer with a relatively high length-to-width ratio would still collapse even though the optical proximity correction method is applied. Consequently, how to improve the method of optical proximity correction to form the needed mask pattern is still an important issue in the field.